Repotting guide

When & how to repot Mountain Sandwort (Arenaria montana)

Also called Mountain Sandwort, Mountain Sandweed.

More about mountain sandwort

About Mountain Sandwort

Arenaria montana · also called Mountain Sandwort, Mountain Sandweed · flowering

Mountain Sandwort is a low-growing alpine perennial from southwestern Europe, forming spreading mats smothered in white star-shaped flowers in late spring. It thrives in well-drained, gritty soil in full sun and is ideal for rock gardens, walls, and path edges. Drought-tolerant once established, it dislikes wet winters and heavy clay soils.

Mature size: 5–10 cm tall, 30–45 cm wide

Watch for — Leggy, sparse flowering: Insufficient sun leads to stretched stems and few flowers. Shear lightly after flowering to keep the mat compact and encourage a second flush of bloom.

How to tell mountain sandwort needs repotting

Repotting on a calendar is less reliable than reading the plant. For mountain sandwort, watch for these signs:

Roots growing out of the drainage holes, or the rootball lifting the plant proud of the rim.
Soil that has shrunk away from the pot sides and no longer holds water.
The pot is unstable because the plant has grown top-heavy.
Old, compacted, broken-down mix that stays wet too long — for a succulent that is a rot risk, so refresh it even if the pot size is fine.

For the underlying biology of a pot-bound root system and why it stalls a plant, see our guide to spotting and fixing a root-bound plant.

How often to repot mountain sandwort

Every 2–3 years, into bone-dry mix. Mountain Sandwort's growth habit — prostrate, mat-forming perennial; spreading stems root as they grow — sets the pace. Mountain Sandwort is a low-growing alpine perennial from southwestern Europe, forming spreading mats smothered in white star-shaped flowers in late spring. It thrives in well-drained, gritty soil in full sun and is ideal for rock gardens, walls, and path edges. Drought-tolerant once established, it dislikes wet winters and heavy clay soils.

What size pot to step mountain sandwort up to

Use a pot only one size up — or even the same pot with fresh gritty mix if the roots have room. Mountain Sandwort stores water and rots in a large pot of slow-drying soil. A tight terracotta pot that dries fast is far safer than a generous plastic one. Never up-pot a succulent by several sizes.

Not sure of the exact diameter? Our pot size calculator takes the current pot and root spread and tells you the right next size — it deliberately recommends a single step up, never a big jump.

The best time of year to repot mountain sandwort

Spring or summer, while mountain sandwort is in active growth and warm, is best — roots recover fastest then, and the plant is not sitting in cool damp soil. Avoid repotting a succulent in winter dormancy.

Step-by-step: repotting mountain sandwort

Repot dry. Do not water mountain sandwort for several days first. Working with dry roots and dry mix dramatically lowers the rot risk for a succulent.
Pick a snug, fast-draining pot. Choose terracotta one size up at most, with a drainage hole. Have gritty gritty, sharply drained, poor to moderately fertile ready.
Tip it out and clean the roots. Slide the plant out, crumble off the old soil, and trim any black, mushy or dead roots with clean snips.
Pot into dry mix. Set mountain sandwort at its original depth in dry gritty mix, firming gently. Do not bury the stem deeper than it was.
Wait a week before watering. Leave it completely dry and out of harsh sun for about 7 days so any damaged roots callus. Only then water lightly.

Aftercare

Keep mountain sandwort completely dry and out of fierce sun for about a week so any nicked roots callus before they meet moisture; watering a freshly repotted succulent is the classic way to rot it. Then resume the normal lean, dry rhythm. Do not fertilise for about 3 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for mountain sandwort

Mountain Sandwort wants gritty, sharply drained, poor to moderately fertile. A mix of loam, coarse grit, and small gravel works best. Avoid rich, water-retentive soils. pH 6.0–7.5. Excellent performer in scree beds or between paving stones. Amend heavy clay with up to 50% grit. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting mountain sandwort — frequently asked questions

How often should you repot mountain sandwort?

Every 2–3 years, into bone-dry mix for mountain sandwort. Repot mountain sandwort every 2–3 years into a snug pot of gritty, sharply drained, poor to moderately fertile, ideally in spring or summer. Let it sit in dry soil and do not water for about a week afterwards so any nicked roots can callus. Over-potting and watering straight away is what rots succulents.

What size pot does mountain sandwort need?

When is the best time of year to repot mountain sandwort?

Should you water mountain sandwort after repotting?

No — not straight away. Repot mountain sandwort into dry mix and wait about a week before the first watering so any damaged roots callus over. Watering a freshly repotted succulent is the single most common way to rot one.

Should you fertilise mountain sandwort after repotting?

Not immediately. Wait about 3 weeks after repotting mountain sandwort. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.